In the construction and mining industry, large power driven machines carry wheels or chains on which are mounted spaced mining blocks which carry contact tools called mining bits. The blocks have cylindrical recesses to receive the mounting shank ends of a bit, and the cutting or abrading part of the bit projects from the mining block.
It is generally desirable to have these mining bits rotate in the receiving block to equalize the wear around the cutting end. One of the problems in this field has been the wear on the mining blocks which, while replaceable, need to have as long a life as possible to eliminate downtime on the expensive machines. A mining bit can be replaced in minutes if it is broken or worn, but it takes considerably more time to replace a mounting block. Of course, one of the problems in the use of these bits is the abrasive character of the fines and dust which are inherent in the earth or coal cutting operation.
Some years back these mining bits were relatively straight cylindrically shaped bits which were supported at the base ends by a strap or stirrup at the base of the hole in the support block. This type of bit and holder is illustrated in a U.S. Patent to Krekeler, U.S. Pat. No. 3,397,012 (Aug. 13, 1968). A little later a wear collar was utilized in the mounting blocks in which a wear shoulder was formed midway between the ends of the wear collar to engage a shoulder in the block recess. This is illustrated in the U.S. Patent to Kniff, U.S. Pat. No. 3,499,685 (Mar. 10, 1970), now U.S. Pat. No. Re. 29,900. A development from this was a wear shoulder intermediate the ends of the tool shank itself cooperating with a shoulder within the block. This is illustrated in a U.S. Patent to Kniff, U.S. Pat. No. 3,650,565 (Mar. 21, 1972). Another approach utilized a conical shoulder between the cutting end and mounting end of the mining bit which bore on a conical chamfer at the mouth of the block recess. This is illustrated in the U.S. Patent to Engle, U.S. Pat. No. 3,519,309 (July 7, 1970).
Another significant factor in the design of these bit and block combinations is the need for retention of the bit within the block. Whatever design is utilized, there must be a retention ring externally or internally of the block recess.
The present invention contemplates a bit and block design which is compatible with an effective retention system and which removes the bearing surface from the mouth of the block recess to the base of the tool shank. The object of the invention is to provide a construction which will minimize or eliminate the wear at the mouth of the bit opening in the block. With the commonly used structure in use, the thrust is against a conical chamfer at the mouth of the block opening. The pressure from the material being cut drives the bit back into the block which, in turn, distorts the bit seat and increases the wear on the shank hole itself. This causes varying heights of the cutting bits and results in a worn out block.
The present invention is directed to a structure in which the load support is transferred to the base of the block recess and the base of the bit. This area is isolated as much as possible from the abrasive fines resulting from the mining operation. This also removes the pounding and stress at the mouth of the opening and still permits rotation of the bit to equalize wear on the bit itself.
Other objects and features of the invention will be apparent in the following description and claims in which the invention is described together with details to enable persons skilled in the art to practice the invention all in connection with the best mode presently contemplated for the invention.